1. Field of the Invention
The present invention relates to a vehicle driving support apparatus that prevents an occurrence of a pitching vibration before and after a vehicle stops due to an operation of an automatic braking.
2. Description of Related Art
A driving support apparatus represented by an ACC (Adaptive Cruise Control) system or a pre-crash control system conventionally often employs an onboard camera or a radar device as a unit for monitoring an environment in front of a subject vehicle. The ACC system controls a vehicle speed, following a preceding vehicle that is travelling in front of the subject vehicle. When it is determined that the subject vehicle approaches rapidly to the preceding vehicle, and a target inter-vehicle distance cannot be maintained with engine braking, the ACC system operates an automatic braking in order to bring the inter-vehicle distance back to the target inter-vehicle distance. On the other hand, the pre-crash braking system determines a possible collision with an obstacle in front of the vehicle, (hereinafter referred to as an “obstacle ahead”), including the preceding vehicle, and when it determines that the collision is unavoidable, it operates the automatic braking so as to avoid a collision.
Japanese Patent Application Laid-Open (JP-A) No. 2008-120141 describes a technique involved with an operation of an automatic braking system as described below. Specifically, when it is determined that the preceding vehicle is substantially stopped, a deceleration for allowing the subject vehicle to stop at a set position is obtained according to the distance between the subject vehicle and the preceding vehicle, and the automatic braking is operated with a braking pressure according to the deceleration.
In the technique described in JP-A No. 2008-120141, the braking pressure is set based upon the distance between the subject vehicle and the preceding vehicle. Therefore, the braking pressure is not reduced before the subject vehicle stops, whereby the front part of the subject vehicle greatly sinks down, which is called a nose dive, immediately before the subject vehicle stops. Upon the stop, a swinging-back occurs as a reaction of the nose dive. The nose dive and a pitching vibration caused by the swing-back thereof give an uncomfortable feeling to a passenger.
A possible solution for preventing the pitching vibration is to temporarily reduce the braking pressure immediately before the vehicle stops. However, in order to efficiently suppress the pitching vibration, the timing of reducing the braking pressure has to be set based upon a road condition (snowy road, icy road, dry road) and the weight of the subject vehicle.
In this case, an additional sensor is required for detecting the road condition or the weight of the vehicle, which not only makes a control complicated, but also increases the number of components, leading to a cost increase.